Vapor-compression distillation



Filed Dec. 12, 1945 2 Sheets-Sheet 1 INVENTOR Geo/we RLu/vr BY ATTORNEYS Nov. 15, 1949 G. P. LUNT VAPOR-COMPRESSIQN DISTILLATION 2 Sheets-Sheet 2 Filed Dec. 12. 1945 INVENTOR GED/76E P. LU/VT ATTORNEYS Patented Nov. 15, 1949 :This invention relates to apparatus; for

improvements in distillation'ofithe vaponcom- :pressiom type,-. namely, a distillation: operation 'wherein':vapor evolved' from a solutionwundergoa x B QZY. PISII ZWION George l i-Lunt wlcllesley Masa, assignort i Ar hu D-,' itt e,,, m 1dse. M sa o 7:.- neraiieaei.M awa December 12, 1945-," sar'a ;1- ro. e i* '03 l 'dlainis. (Cl; 20

, and Y method of'1distillation',and relates particularly to ing distillation is compressed until its condensing n temperature isabove the boiling point of the'solutlon; and is "thereafter condensed in out-of contact heat exchangerelation with the solution to give-up its lieatiof vaporization' to the boiling :solution.*- i

The term-*distillation" is Y used hereinin: 5a broad sense inreference to operations which are L commonly referred-to as evaporation, fractionation; rectification,-=' concentration and the like,

and which are characterized by the evaporation ,ofa portion-of aliquid mixture'for the purpose of separating two-or more substances by reason of "their differences in boiling point orvolatility. Any such mixture which is liquid during some portion ofthe process is' referred to herein, for the i =2 sake'of brevity, as a -solution',' and maybe any more or less-concentrated solution of solids, liquids'or gases in liquids, or liquid mixtures of materials normallyin'the solid or gaseous form in thepurestatem I I In a distillation operation of the vapor-compression type,--" the primary source of energy is supplied in the form of mechanical power used to operate the compressor. 9 "A distillation operation I of the vapor compression type can be successfully carried on using the power supplied to operate he compressor-as the sole source'of energy; but n such case experience 1 has shown that heat osses must be carefully husbanded by efiecting las omplete heat transference as possible-between ncomingand outgoing "effluents and by thoroughly insulatingth'e parts o'f the-apparatus that are operated above norm'alatmospheric tempera- -ture."

t. v. Inorde'rthat less stringent precautions against 5 heat losses may be exercised, thereby minimizing the cost-of construction of distillation apparatus of the-type in question "and facilitatin its operation, sensibleheat may besupplied to the system compression type by anov'el apparatus and method whichhas' the advantage that it does not disturb the I normal functioning of the: system and avoids occurrence of scale deposits, i-corrosive action; and other difliculties." If, I for? example,

the heating element used'toheatthe solution to to compensate for heat los'sesand to maintain the system inproper operational balance. f

be distilled is in direct contact therewithpithe.

' tendency to scale formation is encountered=, -'for practically allzliqfiids-which are distilled have a atendency'to, scale th'eheating surface;- ;-Many liquids undergoing distillationlikewise-haveat-corrosive effect upon the heating surfacearequiring 1 the interior 9 1 use of-specialmaterials and special constructions.

According to the "present invention; such diflisculties'have been overcome' 'whil at the same time i jsensibla :heat -may' besupplied to: the solution undergoing distillatiomu -.It'=is:a featurefof this invention thatin av vapor compression distillation system, improv'edzniea'ris aare -provided whereby" the condensate resulting hfron'i condensation 1 of: compressed vapor Iain "the condenser heat exchanger is. heated so .asto cause evolution. of' vapor lfromx'such 1 condensate :"and whereby the: evolvedav'apor ls 'conden'sed' in out-ofcontacti lieat'w exchange 1 relation with 1 solution within the vaporization chamber so. astO supply .ithet heat of condensation :ofythe vaporized condensate to the solution withinthe vaporization chamber.- According :to :thistinvention this is fi-accomplished' by .the provision .of means :whereby the condensate that is-rformedin the condenser heat. exchanger is collected and brought into contact-with a-heatingelementthat presentsza' heated surface so as toaregenerate vapors which are -reconde'ns.ed in out=of-contact-- heat 1 exchange a relation with solution.undergoing-distillation.in the vaporization chamber. :By this arrangement a simple refluxingscycle can'be maintained wherein 1 the condensate is vaporized: and wherein" the vapor F so'- produced is :recondensedand returned I by gravity to the heatinggelementp By utilizing gravitational fiowfor a. bringing condensate into contact w-ith'rthe heatingelement. any mechanical devicessuch as pumps,icompressors; or the like, can 1 be eliminated and a simple system for! heat transference can be provided" wherein the: con- 'densateandvapor evolved therefrom act as the heat transfer mediumzfor transferring heat from the heated: surface to solution undergoing distillation in the; vaporization chamber.

the heat transference is-accomplished by utilizing Preferably a cycle; wherein the condensate that is formed in the condenser heatexchanger-comes into contact iiwith'thei heated surface by; simple gravitational flow and the;vapors resulting fromthevaporizationof the} condensate arevreconden sedin the :condenser heat exchanger-itself and can .flow back ,forcontact-withthe heatedsurface. x g be accomplished-by locatin a. heating element in This may v f he @Qn n erheatx h n e i self and at a point 'where' the condensatejfo'rmed in they condenserheat exchanger will come incona w th" Al rn ti e jt fl ildt nw ma b collect n a s m 9 g gt g ambr thatis outside the condenser heat exchanger and from Which'the vaporsform ed-"by conta'ctfvvith '-the*heated surface of the heating element' return forcond'ensation' in out-of-co'ntact heat exchange -relation" with solution'in the vaporization cham- 'ber, *-'suc'h vapors preferably beingr reintroduced into the condenser heat exchanger itself. 5; .By any a of the foregoing: arrangements the heated surface 30f the: heating element i mamta n pu zo e'con- 3 tact with the solution in the vaporization chamber and the condensate and vapor evolved therefrom are used for heat transference in a manner that is eifective and simple and does not interfere with the operation of the system as a whole.

Further purposes, features and advantages of this invention will be apparent from the following description of a typical embodiment of the invention in connection with the accompanying drawings, wherein:

Fig. 1 is a schematic elevation of a distillation unit embodying the present invention;

Fig. 2 is a schematic elevation showing the lower portion only of the vaporization chamber of the distillation unit of Fig. 1, in combination with an alternative form of collecting chamber;

Fig. 3 is a schematic elevation similar to Fig. 2 and showing an alternative means for causing vaporization of condensate formed in the condenser heat exchanger, Fig. 3 being on the line 3-3 of Fig. 4;

Fig. 4 is a plan view largely in section of the embodiment of this invention shown in Fig. 3 and taken on the line 3-4 of Fig. 3.

Referring to the accompanying drawings, and particularly Fig. l, the boiling of solution in order to separate vapor therefrom takes place in the vaporization chamber l. The evolved vapor is directed by the low pressure vapor line 2 to the compressor 3 which is adapted to compress the vapor to a pressure such that the condensing temperature of the vapor is above the boiling point of the solution and which is operated by any suitable source of power such as the motor 8. While a rotary type compressor is shown, any other suitable compressor may be employed.

The compressed vapor is directed by the compressed vapor line 5 to the condenser heat exchanger which is indicated generally by the reference character 6 and which is shown as consisting of a plurality of vertically disposed tubes 1 within which boiling solution rises and which are surrounded by the condensing vapor directed into the condenser heat exchanger by line 5. The unvaporized concentrated solution is recirculated by passing downwardly within the downcomer 8. While one type of typical condenser heat exchanger has been shown in the drawing, any other type of condenser heat exchanger adapted for condensing vapor in out-of-contact heat exchange relation with a boiling solution may be employed. Due to the relatively small outlet for condensate from the condenser heat exchanger and the frictional resistance of the condensate in the efiluent line, the desired back pressure for maintaining the condensing temperature of the condensing vapor above the boiling point of the solution is maintained. Alternatively, in instances where the construction or the operating conditions are such that condensate volume is below the full capacity of the eflluent line II, it is generally desirable to provide a steam trap in the efliuent line.

Fresh solution to be distilled is fed into the vaporization chamber by the line 9. Concentrated solution is taken from the vaporization chamber by the line It, and the overflow level 4 I eiiluent hot condensate and hot concentrated solution as in the preheater heat exchanger l2.

Distillation'apparatus of the vapor compression type, as thus far described, is known and for this reason has been shown merely schematically in connection with a typical unit: It is apparent, however, that distillation apparatus of the vapor compression type may take many different forms. According to the present invention, sensible heat is supplied to the vapor compression distillation system in the novel manner and using the novel apparatus described below and illustrated in the accompanying drawings. Referring to the embodiment of this invention shown in Fig. l, a collecting chamber I3 is provided, which is sup-- plied with condensate from the condenser heat exchanger 6 by gravitational flow through the line It. The rate of flow of condensate into the collecting chamber is controlled in any suitable manner as by means of the valve l5, which may be manually operated or which may be automatically operable responsive to the level of liquid within the collecting chamber, e. g., by means of a float (not shown). Alternatively, the rate of how may be maintained at the desired rate by predetermined selection of the flow capacity of the line It. As shown, the draw-off line II is connected to the' condenser heat exchanger 8 slightly above the bottom thereof so as to provide a supply of collected condensate in the bottom of the condenser heat exchanger for being taken off by line H to the collecting chamber IS.

The liquid within the collecting chamber is heated in any suitable way, as by means of an electrical heating unit [6 of the immersion type, although any other heated surface, e. g., provided by steam coils or the like, may be employed. The vapor that results from boiling of liquid within the secondary vaporization chamber 13 is directed by the line I! to the interior of the condenser heat exchanger 6 wherein the vapor becomes commingled with the vapor entering the condenser 6 by line 5. Suitable control means for controlling the amount of heat supplied to the heating unit in the collecting chamber may be provided as desired. Thus, in the case of the electrical heating element IS, the power supplied thereto from the electrical power supply lines 29 may be controlled by means of a control device 30, which may for example be a rheostat, or preferably a series of switches operating to switch on or off portions of the heating element It which would accordingly be in the form of multiple heating units. If some other source of energy is used such as steam, a similar control can be effected as by the use of a suitable valve.

The collecting chamber i3 is desirably pro vided with a sight glass 31 for indicating the liquid level therein. A line l8 controlled by valve l9 may also be provided for initially introducing liquid to be vaporized into the collecting chamber, which is ordinarily desirable at the commencement of a distillation operation.

The vaporization chamber and other parts of the unit ordinarily are covered with thermal heat insulation material (not shown) so as to minimize heat loss, but in the practice of this invention the completeness of the heat insulation can be reduced while still maintaining the desired heat balance in the system.

In the operation of the above-described apparatus, the condensate which flows from the condenser heat exchanger 6 to the collecting chamber is vaporized and returned tothe condenser heat exchanger for condensation therein. In such case,1lll ofithelcondensaitemroduced sinzthesglist lationiappara'tu" '"isluiltiin'ately withdrawn by zthe: line I- l-1 thivalve 8 the'rein' bingsiaupenr'iandthe valve-28 z-inzgline 211- .ibeing closedzi. If desired. .all f" theicondensalteicondensedlinl'th ndensergl-beati exchanger" nmayss be r-takexiasto he collecting chambergw by-the Lline l 'iompar'tial :revaporiza tion ofthe tcoiidensateflandwith returns 'ot j 'ifeva i p'orized? con'de'nsaiter to*thei condenser-": h'eatz ears changer, and the condensatemayf be with'drawn fromtthe system taking it :fr'omi the' collecting chamber: by :.-the v:lineii 2 1., -.the: .va=lve- 2 8 'thereinf bBiIIgln-ZODBI! :and the? valve 38 invlinefll fbeinfi clos'ed'i Ind-each: of the i arrangements above (le -j" scribed it; apparent: that the I-condiansat'e'f the collecting chamber?! 3 and; the' va'por evolved therefrom is; rcontinuouslyli';maintained "*a "e pressure; prevailing withim the condenseriheat' exchanger 6 andithat #the indirect heat trans?"- feren'c'e I is i'maintained merely by gravitational refluxing .of'= 'the condensatei 'Moreover; each-f arrangement is suchthat the' indirect heat transference' can be maintained independentlyof the' withdrawal 1 of 'cond'en'sate' from the system 'and even when the withdrawal} of condensate i from The above-described apparatus represents aj preferred embodiment of this inventionb while it' is' inuch to be 'preferrd 'that the vapor evolved in the-collecting chamber be discharged into 'tli' ddrldehsi heat exchan er B' ior (btllttiefl's'atidrl m enact-contact heat exoliang'e relatl m w'ith thc solution in the primary vaporizationchamb'e' I anyothermeans "for-'dire'ctirig the" vapor ge'ner ated in the "collecting jchamber" I 3 mto'outr; 1 contact heat exchange -"relation'" with solutionf within"'the'vaporizatmn chamber" -ma beam-'- ioyea 'rnus, "by closing "t iewawe in li en; the vaporcan' be directed by? l ne zl thiou'gncoil 22 for condensation in" out-of-cbntactheat exchangerelation With-solution within the vapor-"L izsuon' chamber (the lin'il'bein'g' show'n s che coil 22 mustbe such-that,thecondensing temper-p ature of the vapor is-abovezthe boiling point oi" the solution in chamber 1. However, by connect ing the line 2.3 to the; line I l,;as shown; the' back pressure provided .bythe,iirictionalrresistance Joir:

the preheater heat-- exchanger, J2 is ordinarily;

sufficient to insure acOndensation of ;the a vapor, produced by; boiling the :cpndensate in the. col

lecting chamber-'13, in the;;coil r22;;,and .the-em-L ployment of-o a pressure-relieftyperof valve ,suchasthe va1ve=24 is not necessary: Ifthe-.conde'nsate formed in-"coil 22 is returned ,tohthelcollecting chamber.;l3 'byvline -2B,':the' "desired vpressure is automatically maintained embodiment- 1whereir vapors ev'olved 1.1from' con densate are rcondensed vin icoil 22;:any*make-up liquid can be supplied .:to .the collecting chamber '3 by line 'I 4' or by line I8 ori-by :both, as' may be' desired. *il While such alternative embodiment may" be:emp1oyed;. the valve"20; the: -rcoil 22 'and the lines- 21; 23 andv 2fiwareiomitted sinrnormal prac In rthe :Ialternativemtrbducing vapbrs rrom the o lsmtothe vspor nne sg 'rhe 'bperation or the ression distillation or: this""l nve no -ma'i' illustrated 'asfo1low Liquid, whiehqis orqmarny 1 identical with the"liquid "to be recovereizl I? as" disfirst"-introducd--'mto the v 3 'and oluti'o'n to) tilled 'is' infifdduCd" H tl l' OlizatiOn Chain l i The heat" is -sll ppiid the heating llillli [8; which "causes the liquid in'f the collecting-- chamberal 3 to boil} thereby su and which c'o'ndensesthereing of vaporization the solution-in chamber' li The? compres or is likeivise -placed anopemuon so th'at'piasi soon as" the heat supplied' tdthe $6111 tioni'i inirchamber l causes tl'ie" solutioi i tlo g i v llfi a substantial amount of vapor, such vapor will be: icompresserl *"anli returhed 't0--the' cor denser 1 Eventuallv the rateof'dlS- s increase until the desiied operating" conditions are atta' d; the suppl y br wed-and the:wit-hdrawal'iof oncentr'ated solutionbeing maintained at the desired rate, 'tneiheat supplied;

byaithe heatingmnit l6 being regulatd s ofas maintain the properthermal System:

ct'l hejmethodfand apparatus of-this invention may be'advanta'geously employed in-the recovery of-x' dlstilled potable water from? sea "water; f "In order to afiord-aspecific example of tlie practice] of vthis invention, "the application or *this i'nven tion" the distillation -of sea water is described below 'gj r j] {5; ..fIrt -L 2- I" "Upon-:1 starting up the" is'tillation operation; distilled "water is used todriitially' fill "th 'colle ct ingi-chamber l3" andcold sea" water is-run into" theztvaporizatibn I chamber I" untir the 3 normal: liquid level is reached. The heating element 16* is then tiner 'gizedftdfboif Y the "distilled water-"in the secondary vaporization ch'aiiitierand the compressor is started "The sea water mulevaporization chamber isthereby 1 brought up to itssboiling'lpoint and the normal conditions for a lance in he 1 continuous distillation= o eration" are established;

whereupon the' fee'diof fresh sea water is Started and-.distillate and concentratedfsolution"are with 1 drawnfiom the' sys'tem'. During "a 'ti pi'cal 'continuous distillation operation the incoming 'fe ed of=:.'"sea.water is preheated I in he preheater heat t -..;the compresso1 r= 3 whichboosts the 7 pressure toi3 to fi'poundsper square mcrrgaug pressure formintroduction linto the co'fidenser heat 'ex changer fi wherei'n it condenses and gives up-its] vaporization chamber 1 I The -resulting cond'ensatesis taken f-rom the condensei heat ex'changer 61" o the preheater heatexchanger' l2 .at=a-tem p' pplyini zfvapor'whichace-mu About two-thirds of the sea water fed into the system is vaporized in the vaporization chamber I and about one-third is taken from the system as concentrated solution or brine which enters the preheater heat exchanger ii, at a temperature of the order of 214 F. The distillate is cooled in the preheater heat exchanger I! to within about F. of the temperature of the incoming feed and the hot concentrated solution is cooled in the preheater heat exchanger I! to within about 30 F. of the temperature of the incoming feed. In order to compensate for heat losses which take place in the system, sensible heat is introduced into the system, this being accomplished according to the present invention by boiling a portion of the condensate and condensing the vapor thus produced in out-ofcontact heat exchange relation with the sea water in the vaporization chamber I. In a unit of the character described producing about 50 gallons of distilled water per hour, it has been found to be advantageous to consume about 3.4 to 4 kilowatts per hour for operating the compressor 3 and about 3 to 3.5 kilowatts per hour for supplying electrical energy to heat the electrical heating element It which is in direct contact with the condensate in the collecting chamber l3.

In connection with the foregoing description of distillation of sea water according to this invention, it may be mentionedthat sea water has a pronounced tendency to deposit scale and also has a corrosive effect on ordinary. heating units placed in direct contact with the solution within the vaporization chamber. Whenthe distillation of sea water was carried out according to this invention, no difllculty was experienced from scaling or corrosion. Moreover, the distillation unit was readily adjusted for maintaining distillation at the desired rate while compensating for heat losses by supplying heat to the main heat exchange surfaces of the condenser heat exchanger through the expedient of bringing condensate formed in the condenser heat exchanger into contact with the heating element in the collecting chamber, reboiling of condensate therein, and then recycling of the resulting vapor for condensation again in the condenser heat exchanger.

It is apparent that the practice of this invention can be varied. An embodiment of this invention which is somewhat simpler in construction than the embodiment shown in Fig. 1 is shown in Fig. 2. In Fig. 2, the lower portions only of the vaporization chamber i and of the condenser heat exchanger 6 are shown, it being understood that, except for the collecting chamber arrangement, the distillation unit is the same as that shown in Fig. 1.

In Fig. 2, the collecting chamber 3! is arranged with reference to the condenser heat exchanger 6 so as to be maintained in a flooded condition, since it is in open communication with the lower portion of the condenser heat exchanger 6 below the normal liquid level therein by the wide diameter connection 32. Within the collecting chamber is the heating element 33 which is shown for purposes of illustration as an electrical heating element supplied with power from the supply lines 29 through the control device 30. It is apparent that condensate collected in the condenser heat exchanger 6 will collect in collecting chamber 3i where it can be vaporized by supplying heat to the heating element 93, the evolvedvapors being free to bubble up through the liquid condensate and to escape through the connection 32 into the interior of the condenser heat exchanger 8 for recondensation therein. In Fig. 2, a baiile I4 is shown for the purpose of assisting circulation of liquid within the collecting chamber 3|, but such bafile can be omitted if desired and is not essential. Make-up liquid can be supplied to the collecting chamber 3| by the line OI controlled by the valve 38 during the institution of distillation.

In Figs. 3 and 4, a further alternative embodiment of this invention is shown wherein a collecting chamber separate from the condenser heat exchanger is dispensed with and wherein the lower portion of the condenser heat exchanger itself afiords the collecting means for bringing condensate formed within the condenser heat exchanger into contact with a heating element. An embodiment of this invention, such as that shown in Figs. 3 and 4, is particularly suitable in the case of relatively small-size units. In Figs. 3 and 4, the lower portion only of the vaporization chamber I and of the condenser heat exchanger 9 is shown, it being understood that the parts shown are comprised in a distillation unit such as that shown in Fig. 1 except that there is no collecting chamber located on the exterior of the condenser heat exchanger.

According to the embodiment of this invention shown in Figs. 3 and 4, the heating means is disposed adiacent the bottom of the condenser heat exchanger 6 below the normal liquid level of condensate collected therein and is shown for illustrative purposes as a plurality of electrical heating elements 39 which project inwardly into the interior of the condenser heat exchanger 6 into spaces between the tubes 1 of the condenser heat exchanger. The heating elements 99 are supplied with electrical energy from the power supply lines 29 controlled by the control device 30. It is apparent that in the operation of the embodiment of this invention shown in Figs. 3 and 4, the body of condensate collected in the bottom of the condenser heat exchanger 6 may be boiled by heat supplied by the heating element 39 and that the vapor evolved from the condensate will recondense within the condenser heat exchanger and give up its heat of condensation to solution within the vaporization chamber by out-of-contact heat exchange.

While this invention has been described in connection with certain typical embodiments and examples of the practice thereof, it is apparent that variations may be made without departing from the scope of this invention as defined by the language of the fololwing claims.

I claim:

1. The combination with distillation apparatus of the character described comprising a vaporization chamber, a compressor, means for directing vapor evolved from solution in said vaporization chamber to said compressor for compression therein, a condenser heat-exchanger within said vaporization chamber arranged to condense vapor in out-of-contact heat exchange relation with solution within said vaporization chamber, means for directing vapor compressed by said compressor to said condenser heat-exchanger for condensation therein, means for feeding solution to be distilled into said vaporization chamber, means for withdrawing concentrated solution from said vaporization chamber, and means for withdrawing condensate from said condenser heat-exchanger and from said distillation apparatus; of heat transfer means for transferring heat to soluin out-of-contact heat exchange relation with solution within said vaporization chamber, means for directing vapor compressed by said compressor to said condenser heat-exchanger for. condensation therein, means for feeding solution to be distilled into said vaporization chamber, and means 'for withdrawing concentrated solution a from said vaporization chamber; of a collecting chamber outgde of said condenser heat-exchanger, means for directing condensate from said condenser heat-exchanger to said collecting chamber, heating means for heating liquid contained in said collecting chamber to cause evolution of vapor therefrom, means for directing vapor evolved from liquid in said collecting chamber into out-of-contact heat exchange relation with solution in said vaporization chamber for condensation while in said heat exchange relation, and means for withdrawing condensate from said collecting chamber and thence out of the distillation apparatus.

9. The combination with distillation apparatus of the character described comprising a vaporization chamber, a compressor, means for directing vapor evolved from solution in said vaporization chamber to said compressor for compression therein, a condenser heat-exchanger within said vaporization chamber arranged to condense vapor in out-of-contact heat exchange relation with solution within said vaporization chamber, means for directing vapor compressed by said compressor to said condenser heat-exchanger for condensation therein, means for feeding solution to be distilled into said vaporization chamber, means for withdrawing concentrated solution from said vaporization chamber, and means for withdrawing condensate from said condenser heat-exchanger and from said apparatus; of a collecting chamber outside of said condenser heat-exchanger, means for directing condensate from said condenser heat-exchanger to said collecting chamber by gravitational flows, heating means for heating liquid contained in said collecting chamber to cause evolution of vapor therefrom, and means for directing vapor evolved from liquid in said collecting chamber into said condenser heat-exchanger for condensation in out-of-contact heat exchange relation with solution in said vaporization chamber.

10. In apparatus of the character described, the combination accordin to claim 9 which comprises means for directing liquid other than condensate contained in said condenser heat-exchanger into said collecting chamber.

11. In a method of distillation wherein solu tion to be vaporized is introduced into a vaporization zone, vapor is withdrawn from said vaporization zone, the withdrawn vapor is compressed until its condensing temperature is above the boiling point of the solution in said vaporization zone, the compressed vapor is condensed in a condenser heat-exchanger in out-of-contact heat exchange relation with solution in said vaporization zone, concentrated solution is withdrawn from said vaporization zone and out of the system, and condensate is withdrawn from said condenser heat-exchanger and out of the system; the supply of heat to solution in said vaporization zone by the steps comprising directing condensate formed in said condenser heat-exchanger by gravitational flow into contact with a heated surface, vaporizing condensate thus contacted with said heated surface, and recondensing in out-of-contact heat exchange relation with solution in said vaporization cham- I ber substantially all of the vapor thus produced. 12. In a method of distillation according to claim 11, the supply of heat to solution in said vaporization zone by the steps recited in claim 11' wherein the vapor produced by heating condensate formed in said condenser heat-exchanger is recondensed in said condenser heat-exchanger.

13. In a method of distillation wherein solution to be vaporized is introduced into a vaporization zone, vapor is withdrawn from said vaporization zone, the withdrawn vapor is compressed until its condensing temperature is above the boiling point ofthe solution in said vaporization zone, the compressed vapor is condensed in a condenser heat-exchanger in out-of-contact heat exchange relation with solution in said vaporization zone, concentrated solution is withdrawn from said vaporization zone and out of the system, and condensate is withdrawn from said condenser heat-exchanger and out of the system; the supply of heat to solution in said vaporization zone by bringing condensate formed in said condenser heat-exchanger into contact with a heated surface to heat and cause vaporization of said condensate, recondensing substantially all of the vapor thus produced in outof-contact heat exchange relation with solution in said vaporization zone, and returning condensate formed by said recondensation by gravitational flow for contact with said heated surface.

14. In a method of distillation wherein solution to be vaporized is introduced into a vaporization zone, vapor is withdrawn from said vaporization zone, the withdrawn vapor is compressed until its condensing temperature is above the boiling point of the solution in said vaporization zone, the compressed vapor is condensed in a condenser heat exchanger in out-of-contact heat exchange relation with solution in said vaporization zone, concentrated solution is withdrawn from said vaporization zone and out of the system, and condensate is withdrawn from said condenser heat-exchanger and out of the system; the supply of heat to solution in said vaporization zone by supplying heat to solution in said vaporization zone by heating condensate formed in said condenser heat-exchanger by contact with a heated surface to cause evolution of vapor therefrom, substantially all of the vapor so evolved being recondensed in said condenser heat-exchanger to form condensate that is refluxed for contact with said heated surface to complete a closed cycle, said condensate and the vapor evolved therefrom being continuously maintained at the pressure prevailing within said condenser heat-exchanger throughout said closed cycle.

GEORGE P. LUNT.

REFERENCES CITED The following references are of record in the file of this patent: v

UNITED STATES PATENTS Number Name Date 760,440 Forbes May 24, 1904 FOREIGN PATENTS Number Country Date 308,736 Great Britain May 8, 1930 OTHER REFERENCES U. S. Army, Corps of Engineers, Technical Manual T. M. 5-2068 Jan. 1945 (pages 8 and 10), 

